US 5122964 A Abstract In a rotary shear line in which sheet stock is fed by a feeder to a rotary shear for fly cutting by its rotating cutting edges, a synchronous speed and a synchronization length are calculated by an arithmetic unit which are supplied with the cutting length and the average feed rate of the sheet stock. Reference pulses of a frequency corresponding to the synchronous speed and the synchronization length are provided to a first numerical controller for controlling the feeder and a second numerical controller for controlling the rotary shear. The first numerical controller controls the feeder to feed the sheet stock at a speed higher or lower than the synchronous speed in such a manner that when the sheet stock is fed at the synchronous speed, the length of the sheet stock short or excessive of the cutting length before its cutting is compensated for within a cutting period. The second numerical controller controls the rotary shear to rotate its cutting edges at a speed higher or lower than the synchronous speed in such a manner that when the cutting edges are rotated at the synchronous speed, the circumferential length of the locus of each cutting edge short or excessive of the circumferential length of its 360° rotation is compensated for within the cutting period.
Claims(9) 1. A rotary shear line comprising:
a feeder for feeding sheet stock; a rotary shear for fly cutting said sheet stock from said feeder by rotating cutting edges; a first motor for driving said feeder; a second motor for rotating said cutting edges of said rotary shear; first numerical control means for controlling said first motor; second numerical control means for controlling said second motor; and arithmetic means which is supplied with an average travel speed of said sheet stock and its cutting length and, based on said average travel speed and said cutting length, calculates a synchronous speed and a synchronization length and then outputs reference pulses of a frequency corresponding to said synchronous speed and said synchronization length; wherein said first control means is supplied with said cutting length, said reference pulses from said arithmetic means and said synchronization length, and controls said first motor so that during a period in which said cutting edges are assumed to rotate by said synchronization length at said synchronous speed, said first motor feeds said sheet stock by said cutting length and before the feed length of said sheet stock reaches said cutting length, the feed rate of said sheet stock reaches said synchronous speed and is held; and wherein said second numerical control means is supplied with a circumferential length of one rotation of the locus of said cutting edges, said reference pulses from said arithmetic mean and said synchronization length, and controls said second motor so that during a period in which said sheet stock is assumed to travel by said synchronization length at said synchronous speed, said second motor rotates said cutting edges by said circumferential length and before said rotation of said cutting edges reaches at least said circumferential length, the rotational speed of said cutting edges reaches said synchronous speed and is held. 2. The rotary shear line of claim 1, wherein said first numerical control means includes: first encoder means for generating pulses corresponding to the feed of said sheet stock; first add/subtract means which creates a first compensation value by subtracting said synchronization length from said cutting length, sets therein said first compensation value for each cutting of said sheet stock, cumulatively adds a predetermined value to said first compensation value upon each application of said reference pulse, and cumulatively subtracts a predetermined value from said first compensation value upon each application of a pulse from said first encoder means; and first velocity reference generating means which adds together said synchronous speed and the output of said first add/subtract means and outputs the result of addition as a first velocity reference signal for controlling the speed of said first motor; and wherein said second numerical control means includes: second encoder means for generating pulses in accordance with the rotation of said second motor; second add/subtract means which creates a second compensation value by subtracting said synchronization length from said circumferential length, sets therein said second compensation value for each cutting of said sheet stock, cumulatively adds a predetermined value to said second compensation value upon each application of said reference pulse, and cumulatively subtracts a predetermined value upon each application of the pulse from said second encoder means; and second velocity reference generating means which adds together said synchronous speed and the output of said second add/subtract means, and outputs the result of addition as a second velocity reference signal for controlling the speed of said second motor.
3. The rotary shear line of claim 2, wherein said first numerical means includes: sheet stock feed rate generating means whereby the frequency of said pulses from said encoder means is output as a sheet stock feed rate signal representing the feed rate of said sheet stock; and first subtract means which subtracts said sheet stock feed rate signal from said first velocity reference signal and outputs the result of subtraction as a drive signal of said first motor; and wherein said second numerical control means includes: rotating speed signal generating means whereby the frequency of said pulses from said second encoder means is output as a rotating speed signal of said cutting edges; and second subtract means which subtracts said rotating speed signal from said second velocity reference signal and outputs the result of subtraction as a drive signal of said second motor.
4. The rotary shear line of claim 3, wherein said first numerical control means includes: first count means in which an initial value is set for each cutting of said sheet stock and which additively or subtractively counts said pulses from said first encoder means in accordance with the direction of rotation of said first encoder means; first signal converting means for converting the count value of said first count means into a velocity signal; first switching means for selectively applying the output of said first velocity reference signal generating means and the output of said first signal converting means as said first velocity reference signal to said first subtract means; and first sign detecting means which detects the sign of the output of said first velocity reference generating means and switching said first switching means accordingly; and wherein said second numerical control means includes: second count means in which an initial value is set for each cutting of said sheet stock and which additively or subtractively counts said pulses from said second encoder means in accordance with the direction of rotation of said second encoder means; second signal converting means for converting the count value of said second count means into a velocity signal; second switching means for selectively applying the output of said second velocity reference generating means and the output of said second signal converting means as said first velocity reference signal to said first subtract means; and second sign detecting means which detects the sign of the output of said second velocity reference generating means and switches said second switching means accordingly.
5. The rotary shear line of claim 2, 3, or 4, wherein said first encoder means is coupled to said first motor.
6. The rotary shear line of claim 2, wherein said first encoder means is provided in rotary contact with said sheet stock.
7. The rotary shear line of claim 1, wherein said arithmetic means sets the frequency of said reference pulses and said synchronization length to be provided to said second numerical control means to values larger than those which are provided to said first numerical control means.
8. The rotary shear line of claim 1, 2, 3, or 4, wherein said arithmetic means includes means whereby, letting acceleration of said rotary shear, acceleration of said feeder, said synchronization length, a circumferential length of one rotation of the locus of said cutting edges, and said cutting length be represented by α
_{S}, α_{F}, L_{S}, L_{SO}, and L, respectively, said synchronization length L_{S} is calculated by the following equation: ##EQU8## and whereby, letting said synchronous speed and the average feed rate of said sheet stock be represented by V_{S} and V_{L}, respectively, said synchronous speed V_{S} is calculated by the following equation: ##EQU9##9. The rotary shear line of claim 1, 2, 3, or 4, wherein said arithmetic means includes means whereby, letting said synchronous speed, the average feed rate of said sheet stock, said synchronization length, and said cutting length be represented by V
_{S}, V_{L}, L_{S}, and L, respectively, said synchronization length L_{S} is calculated by the following equation: ##EQU10##Description The present invention relates to a rotary shear line in which sheet stock is fed by a feeder to a rotary shear for fly cutting by its rotating cutters. FIG. 1 shows a conventional rotary shear line, in which sheet metal or similar sheet stock 11 is leveled by a leveler 12 and is then fed to a rotary shear 13. A line speed V FIG. 2 shows another conventional rotary shear line, in which the sheet stock 11 delivered from the leveler 12 is fed by a feeder 24 at a constant feed rate. The line speed V In the rotary shear line depicted in FIG. 1 the leveler 12 may sometimes be preceded by a plating, annealing or similar processing stage, and in the rotary shear line shown in FIG. 2 the feeder 24 may sometimes be preceded by a processing stage different from the leveler 12. At any rate, the rotary shear line operates on the following principle. The numerical controller 21 controls the rotary shear 13 through the shear motor 17 so that the upper and lower cutting edges 23 are rotated 360 degrees for each preset feed of the sheet stock 11 and mesh with each other at a distance of the preset cutting length from the forward end of the sheet stock 11 and so that the peripheral speed of each cutting edge 23 is synchronized with the feed rate of the sheet stock 11, i.e. the line speed V The rotating speed V In FIG. 4 the curve 28 shows a line speed V Where the cutting length L is shorter than L Where the cutting length L is, for example, 600 mm, however, the shear motor 17 needs only to be accelerated and decelerated for a time corresponding to an adjustment length of 100 mm as depicted in FIG. 5B. In this instance, since the sheet stock 11 must be fed as long as 600 mm throughout the acceleration and deceleration time and the settling time, the line speed V Where the cutting length L is equal to ΞD=L Where the cutting length L is a little longer than ΞD=L For the reasons given above, the V As described above, in the conventional rotary shear line the speed must be slowed down materially for cutting sheet stock into short lengths. Where the line speed is so low that the flywheel effect of the rotary shear including the shear motor cannot be expected yet sheet stock cannot be cut only with the torque of the shear motor--in practice, this often occurs under restrictions on the manufacturing cost of the machine--, the rotary shear may sometimes come to a halt without cutting the sheet stock because of the low line speed, or even if the sheet stock can be cut, the rotary shear almost stops its rotation, with the result that the sheet stock being fed is blocked by the cutting edges and hence it curves into a hump. For the same reasons as mentioned above, the sheet stock cannot be cut into desired medium and long lengths, either, when the line speed is low. Also when the cutting length L is longer than the afore-mentioned circumferential length L A first object of the present invention is to provide a rotary shear line in which the line speed need not be decreased so much as in the prior art in the case of cutting sheet stock into short length. A second object of the present invention is to provide a rotary shear line in which, also when the cutting length is short, the peripheral speed of cutting edges of the rotary shear can be increased to a value higher than the line speed, i.e. a value at which cutting of sheet stock can easily be done by the aid of the flywheel effect. A third object of the present invention is to provide a rotary shear line which permits cutting of sheet stock at the same high speed as mentioned above even if the line speed is low. A fourth object of the present invention is to provide a rotary shear line which permits cutting of sheet stock into lengths larger than the afore-mentioned circumferential length L A fifth object of the present invention is to provide a rotary shear line in which a relatively sufficient settling time can be provided and the feed rate of sheet stock need not be changed with the line speed at the preceding stage and is very stable, ensuring high cutting accuracy. In the rotary shear line of the present invention in which sheet stock is fed by a feeder to a rotary shear for fly cutting by its rotating cutters, the average travel speed of the sheet stock (the line speed) and the cutting length are applied to a numerical controller, which accelerates and decelerates both of the feeder and the rotary shear and then settles them down to a certain speed (which will hereinafter be referred to as a synchronous speed). That is, the present invention attains the above-mentioned objects by accelerating and decelerating the feeder as well as the rotary shear, i.e. by operating them in cooperation with each other. Thus, the feeder is also accelerated and decelerated, but its average speed is the line speed following the speed at the preceding stage and is independent of the above-said synchronous speed. Accordingly, even if the average speed of the feeder is low, the synchronous speed can be increased. FIG. 1 is a block diagram showing a conventional rotary shear line; FIG. 2 is a block diagram showing another conventional rotary shear line; FIG. 3A is a diagram showing the rotating speed of a shear motor when the conventional rotary shear line is in a short-length cutting mode; FIG. 3B is a diagram showing the rotating speed of the shear motor when the conventional rotary shear line is in a medium-length cutting mode; FIG. 3C is a diagram showing the rotating speed of the shear motor when the conventional rotary shear line is in a long-length cutting mode; FIG. 4 is a graph showing, in comparison, characteristics of the rotary shear line of the present invention and the conventional one; FIG. 5A is a diagram showing an example of the relationship between the rotating speed of the shear motor and the line speed in the conventional rotary shear line; FIG. 5B is a diagram showing another example of the relationship between the rotating speed of the shear motor and the line speed in the conventional rotary shear line; FIG. 5C is a diagram showing another example of the relationship between the rotating speed of the shear motor and the line speed in the conventional rotary shear line; FIG. 5D is a diagram showing another example of the relationship between the rotating speed of the shear motor and the line speed in the conventional rotary shear line; FIG. 5E is a diagram showing still another example of the relationship between the rotating speed of the shear motor and the line speed in the conventional rotary shear line; FIG. 6 is a diagram showing one cutting mode of the rotary shear line of the present invention; FIG. 7 is a diagram showing another cutting mode of the rotary shear line of the present invention; FIG. 8 shows the comparison of cutting modes of the rotary shear lines of the present invention and the prior art example; FIG. 9 is a diagram showing a further cutting mode of the rotary shear line of the present invention; FIG. 10 is a block diagram illustrating the construction of the rotary shear line of the present invention; and FIG. 11 is a diagram showing the acceleration and deceleration of the feeder and the rotary shear, for explaining how to determine the synchronization length in the present invention. A description will be given first of various cutting modes which are performed by the rotary shear line of the present invention which will be described later with reference to FIG. 10. A first cutting mode is used when the average line speed V Next, a description will be given, with reference to FIG. 7, of a second cutting mode in which the sheet stock is cut into short lengths (L<L 60/T represents the number of cutting operations per minute. On the other hand, the feeder motor 26 is decelerated below the synchronous speed V In FIG. 8 the curve 29 represents the rotating speed of the shear motor 17 in the case of rotating the rotary shear 13 through 360 degrees to settle it at the line speed V Next, a description will be given, with reference to FIG. 9, of a third cutting mode in which the sheet stock is cut into long lengths (L>L As will be appreciated from the above and comparison of the curves 28 and 31 in FIG. 4, according to the present invention, the capability of the rotary shear line is markedly enhanced as compared with the prior art; therefore, the line need not always be run at the upper limit of its capacity but instead a sufficient amount of time is consumed for settling the rotary shear and the feeder or the acceleration and deceleration are lowered to thereby reduce external disturbance such as mechanical shock, by which the cutting accuracy can be improved. This can be accomplished by the rotary shear line of the present invention shown in FIG. 10 in which desired acceleration and deceleration are shared between the rotary shear and the feeder by operating them in cooperation with each other as referred to previously. So long as the cutting length L is within a range of possible cutting length, the synchronous speed V Besides, a pulse train which represents the apparent feed length of sheet stock is obtained from an oscillator as described later, and hence its count value (corresponding to length) and its frequency (corresponding to speed) are highly stable as compared with the count value and the frequency of the pulses available from the encoder 19 (FIGS. 1 and 2) in the prior art. This also serves to improve the cutting accuracy. Thus, the fifth object of the present invention is achieved. FIG. 10 illustrates an embodiment of the rotary shear line of the present invention, which employs the same line construction as that of the prior art example shown in FIG. 2. The feeder 24 is driven by the feeder motor 26 and the rotary shear 13 is driven by the shear motor 17. The feeder motor 26 and the shear motor 17 are each numerically controlled, and this control is effected by substantially the same system as that disclosed in U.S. Pat. No. 4,266,276, for example. In the system of the U.S. patent reference pulses are provided from a length measuring encoder, whereas in the present invention they are obtained from an oscillator 33. The line speed V The synchronization length L Upon application of a cutting end signal (which is produced by, for example, a sensor or counter (not shown) which detects one rotation of the rotary shear 13), the frequency F There are cases where the velocity references, i.e. the outputs of the adders 37 and 38 become minus because the compensation values N Next, a description will be given of a method for computing the frequency F Even with about the same load factor, acceleration of the feeder can usually be made greater than that of the shear. The load on the feeder is the feed rolls and the sheet stock, and the sheet stock intended to be handled in the rotary shear line of the present invention is a plated sheet metal, surface treated steel sheet, aluminum plate, or paper, and hence is relatively lightweight, but high-speed processing is desirable for them. The feeder itself is also far smaller in weight, because the rolls are hollow and simple-structured. In the example shown in FIG. 4, the acceleration of the feeder is 1.6 times higher than the acceleration of the shear, and the rated speed of the shear is 200 m/min, whereas the rated speed of the feeder is 240 m/min. The acceleration of the feeder is set to about 2 G. By selecting the shape of the loop 27 of the sheet stock 11 at the preceding stage of the feeder, instead of using such a free catenary structure as shown in FIG. 10, it is possible to prevent lateral rocking of the loop when the acceleration of the feeder is 3 G or more and jumping of the sheet stock by sudden deceleration. The following equation is obtained, as an equation for the afore-mentioned condition, from the relationships shown in FIG. 11 corresponding to those at rows A and B in FIG. 7. ##EQU5## where α Thus, the synchronization length L When the line speed V According to the curve 32 in FIG. 4, when the cutting length L is approximately 300 mm, the synchronous speed V The curve 32 in FIG. 4, which represents the maximum possible line speed for the cutting length L, can be obtained by collecting data with the allowable load factor and the allowable rotating speed of the motors in the actual running of the rotary shear line (without using sheet stock). The curve 32 is stored in the arithmetic unit 34. When the line speed V Although the rotary shear line in FIG. 10 is shown to be formed using hardware, the parts except such power units as the motors, the encoders and the drivers, may be formed using software. The motors may be AC or DC motors, and consequently, the drivers may also be vector control type inverters, DC choppers, or thyristor converters. By selecting the synchronization length L The number of pulses from the encoder 44 which are cumulatively subtracted by the adder 39 in the embodiment of FIG. 1 correspond to the feed length of the sheet stock 11. However, when the sheet stock 11 and the feeder 24 slip relative to each other or the rolls of the feeder 24 are deformed by being screwed down onto the sheet stock 11, an error is produced in the correspondence between the number of pulses from the possible to employ, instead of supplying the pulses from the encoder 44 to the adder 39, an arrangement in which an encoder 44a is provided in rotary contact with the sheet stock 11 as indicated by the broken line in FIG. 10 so that pulses corresponding to the distance of the sheet stock 11 traveled are applied to the adder 39. As described above, according to the present invention, the feeder and the shear are accelerated and decelerated in cooperation with each other, by which, even when the sheet stock is cut into short lengths, the line speed V It will be apparent that many modifications and variations may be effected without departing from the scope of the novel concepts of the present invention. Patent Citations
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